Ocean acidification (OA) presents a fundamental challenge to marine biodiversity and sustained ecosystem health. Reproductive and developmental processes are considered to be particularly vulnerable to OA. My PhD research examined reproductive response (measured as nauplii production), cuticle composition and stage specific growth for the copepod Tisbe battagliai over three generations at four tightly regulated pH conditions (pH 7.67, 7.82, 7.95±0.02; pH 8.l±0.06) and for combined impact ofOA and environmentally relevant copper concentrations. As part of my case studentship with the MBA I also examined OA effects on spermatophore attachment and seminal fluid stores in the female reproductive system. A significantly increased naupliar production at pH 7.95 was attributable to an initial stress response which was succeeded by a hormesis- like response at pH 7.67. The significantly decreased naupliar production at pH 7.82 was the first part of a biphasic reproductive response followed by a compensatory increase in naupliar production at pH 7.67 remaining below control levels. This pattern was consistent across all generations and broods. A mixed effects model predicted a gradual decline in naupliar production over the next 100 years (equivalent to approximately 2,430 generations). Growth (mean length integrated across all developmental stages) decreased significantly below control values at pH 7.82, and 7.67. Cuticle elemental analysis indicated significant alterations in oxygen and carbon content as seawater pH decreased. Changes in growth, cuticle composition and nauplii production strongly suggest that when under OA-induced stress copepods will preferentially reallocate resources in favour of maintaining reproductive output at the expense of somatic growth and cuticle integrity. Experiments incorporating additional copper with increasing OA observed significantly increased naupliar production at pH 8.10, this was followed by a significant reduction in naupliar production beyond that of OA alone from pH 7.95, to pH 7.82, and 7.67. Growth significantly increased with addition of copper, compared to OA impact alone. Cuticle elemental composition observed significant reductions in sulphur, phosphorus and calcium concentrations for those copepods subjected to combined OA and copper. Copepods subjected to additional copper with increasing OA were taking up copper which not only increased metabolism observing a significant increase in growth, but also became toxic observed with a significant further reduction in naupliar production. Addition of copper was seen to have an additive detrimental effect on naupliar production and the copepod population as observed from the mixed effects model output. Techniques developed in . ii. confocallaser scanning microscopy enabled the comparison of seminal fluid stores within the female reproductive system. No significant differences were observed between female reproductive structures and seminal fluid stores with increasing OA from pH 8.1 0 to pH 7.67. Spermatophore size significantly decreased with increasing OA, however to the same extent of female copepod size.