biological survey

4. Discussion and Recommendations
Seagrass

Overall, there has been a decrease in the native species of T. testudinum and an increase in the invasive species H. stipulacea. S. filliforme populations appear to be stable, with a slight increase in coverage. Native seagrass Thalassia testudinum (Tt) has had an overall decrease in coverage from 48.78% in 2011 to 20.61% in 2022 . Over this same time period there has been a slight
increase in native seagrass Syringodium filiforme, from 3.85% in 2011 to 6.44% in 2022.

Lastly, there has been an alarming increase in the invasive seagrass Halophila stipulacea, growing from 6.01% in 2011 to 35.24% in 2022. A table with the annual averages for the three seagrasses can be found below in Table 1.

Sargassum has been an issue within Lac Bay, with several of the survey sites being locations where decaying sargassum has created a thick mat, which in most cases was slowly removed with the tide. Physical impact of the sargassum landings can be seen by the seagrass dieback all along the mangrove border from the south until just north of Punto Kalbas. This is noticeable at G.
Additionally, at location E, a very fluffy sediment was found to be covering the substrate. A likely explanation is that this is the result of decomposed sargassum settling at this site. The overall cover by all species together seems to be stable, but in terms of biomass it would appear to be lower. The ecosystem services provided by Halophila stipulacea are significantly lower than those of
Thalassia testudinum due to its shallow root structure (Smulders et al., 2017) and the fact that it is less nutrient rich than native seagrass species (Boman et al., 2019). The shift towards this nonnative species is of concern and should be closely monitored.

Benthic Species
Since 2018 Halimeda species and in 2022 bioturbation observations were added to the methodology of these surveys. Although bioturbators were noted in 2020, they were not quantified in such a way to allow objective, quantitative comparisons moving forward. Overall cover by Halimeda seems to have decreased but a longer time series is required to draw more definitive conclusions.
Two students have looked into carbonate sand production by Halimeda during the Lac Ecological Restoration project: Laura Timmermans (2018) and Valeria Pesch (2019). Results from these studies were inconclusive, highlighting the need for additional research to fully understand the contribution of Halimeda to carbonate sands and infilling of the bay.

In addition, more information is needed on the influence of eutrophication (Slijkerman et al., 2011) on this process. Table 2 below shows the overall averages for both species of Halimeda from 2018 to 2022. Table 2: Overall Halimeda averages between 2018 and 2022.

Sand particles size in Lac was measured during the Conch Stock Restoration project. Largerfractions often show Halimeda segments next to small shells and other carbonate particles(Figure 5). For this reason, it is believed thatHalimeda sp.are a major contributor of sandwithin the bay.

Sediments have been analyzed for carbonate content in several other studies such as theEHLZK projectand duringthe baseline surveys conducted in 2012 (Debrot et al, 2012).Although the findings have not been published, the data showed that sediments towards thecenter of the bay have a higher CaCO3content, and the distribution sand, silt, clay changes(Appendix VI). In addition, it was foundthat terrigenous sediments were most prevalent alongthe borders of Lac-mainly in the northwestern sector, whereas endogenous sediments werefound in the central part of the bay and towards the reef. 

Bioturbators have also been added to recent surveys as it is believed to be important as itmay cause a loss of sequestered carbon, and new sediment may facilitate settlement ofH.stipulacea. Bioturbators are considered to be ecosystem engineers, changing the substratelandscape.Common bioturbators are callianassid (burrowing ghost) shrimp, the lugworm,mantis shrimp and the burrowing sea cucumber.

1. BackgroundInvertebrates play a critica

l role in maintaining a resilient and healthy environment. These speciesare one of the most globally abundant and diverse animal groups, comprising nearly 80% of alldocumented species to date (Brusca &Brusca, 2002). In fact, these species occupy a wide range oftropic levels, interacting with species throughout the food web.One study (Prather et al, 2020) broke down the importance of invertebrates into the following fourecosystem services:

1) Supporting services. This includes primary production, decomposition, nutrient cycling,hydrologic flux and habitat formation and modification. Within the sediment, invertebratescan dramatically influence water movement, increasing soil porosity (Derouard etal., 1997)and decreasing litter quantity (Wardle, 2002).

2) Providing services. These contributions include serving as a food source, or generatinghousehold goods, inclusion in biochemical or pharmaceutical products as well as a boundlesssupply ofscientific study. For Lac, thequeen conch is an iconic species, whose meat washistoricallyfeatured in local cuisine and shellis still usedas decoration.

3) Regulating services. This includes ability to improve water quality, food web stability,disease regulation within populations as well as pest and invader control. In shallow marineecosystems, bivalves (such as mussels and oysters) can provide substantial water filtrationthroughout the water column.

4) Cultural services. This includes benefits obtained from recreational services and theircultural significance. Many iconic invertebrate species, such as octopus, corals, sponges andconch create a vibrant landscape for scuba divers and snorkelers alike to explore.

Lac Bay has great economic,environmental and cultural value, none of which would be possiblewithout a healthy and robust invertebrate population. These invertebrates are help build resiliencewithin the sandy plateaus, seagrass beds and mangroves, serve as a point of interest forvisitors, andareeither themselves iconic, or vital to the success of other iconic species (such as the flamingo andsea turtle)within the bay.

Historical Data

A study conducted in 1969 by Hummelinck and Roosgave the first qualitative data forqueen conch general distribution throughout Lac Bay. In 2000, a study by Lottpresented the first quantitative data within the same study area. This was followed by asecond survey in 2007. From 2010 onwards (Conch Stock Restoration Project)assessment of queen conch population has been done at irregular intervals (2010,2013, 2015, 2016, 2020).

Results
A total of 43,200 m2 was surveyed and 85 live conchs were found and measured. This resulted in a population density of 19.27 conchs / Ha. To use the Allee effect, only sexually mature conchs should be considered. Over the course of this study, no sexually mature conchs were found , the oldest conch had a lip thickness which measured 6 mm.

Below, Table 1 has been included to summarize the results of the last 5 surveys (2010, 2013, 2015, 2016, 2020). It is interesting to note the dramatic increase between conch populations in 2010 and 2013, and then the rapid decrease in follow on surveys. The results of the 2020 survey highlight a significant issue with only 85 conchs found, none of which having reached sexual maturity. Figure 4 shows a map with the total number of live conchs found per location. There was also a significant number of poached conchs (Table 2/Figure 5) found within the bay. In fact, there were more poached conch shells (100) found than live conch (85), demonstrating that poaching is still an issue which needs to be addressed before the conch population can rebound. 

Each quadrant (quantity 49) equates to 0.09 ha. Using this value, the following densities per year were calculated: 2010 (6.35 conchs/ha), 2013 (51.70 conchs/ha), 2015 (46.49 conchs/ha), 2016 (21.54 conchs/ha), 2020 (19.27 conchs /ha)